The subspecific status of the Yunnan lar, H. l. yunnanensis, is doubtful as it
is likely synonymous with H. l. carpenteri and as such, is not considered as a
subspecies here (Geissmann 1995; Brandon-Jones et al. 2004; Groves &
Geissmann pers comm. cited in Geissmann 2007). Some publications still do
consider H. l. yunnanensis a valid subspecies, however all of this may be moot
as the populations which may have made up H. l. yunnanensis are in all
likelihood extinct (Geissmann 2008). All subspecies need to be better defined
and are not highly distinct (Brockelman & Geissmann 2008).

MORPHOLOGY

Photo: Michael Pogany

Lar gibbons weigh on average between 5.0-7.6 kg (11.0-16.8 lb)(M) and 4.4-6.8
kg (9.7-15.0 lb) (F). Head and body lengths range from 43.5-58.5 cm (17.1-23.0
in) (M) and 42.0-58.0 cm (16.5-22.8 in) (F) (Roonwal & Mohnot 1977). Like
all apes, lar gibbons have no tail and also possess small ischial callosities as
well as long arms suited for brachiation (Ankel-Simons 2007).

Pelage is creamy, brown, or black in both sexes and at all ages (Roonwal
& Mohnot 1977; Mootnick 2006; Bartlett 2009). Adults have a ring around the
hairless face (less apparent in lighter individuals) and have white feet and
hands that contrast with the rest of the body (Marshall & Sugardjito 1986;
Groves 2001; Mootnick 2006; Ankel-Simons 2007; Bartlett 2009). Individuals are
either light or dark in overall color (often called light and dark phases), with
light individuals having buff or creamy pelage, and dark individuals with brown
or black pelage (Groves 2001). The deciding factor whether a lar gibbon is dark
or light is simple genetic inheritance from its parents, in which the dark form
is the dominant allele (Brockelman 2004). The proportion of dark to light individuals
varies in lar gibbons, with some populations being
mostly light and others being mostly dark and with various proportions
in-between, often varying greatly between populations (Marshall & Sugardjito
1986; Brockelman 2004). Mating is random with respect to pelage color
(Brockelman 2004).

H. l. carpenteri are long-haired and almost black or brownish charcoal in the
dark form and are creamy white or white-buff in the light form (Groves 2001;
Mootnick 2006). H. l. entelloides are black or black-brown in the dark form and
honey-colored in the light form with darker legs (Groves 2001; Mootnick 2006).
H. l. lar are medium brown or dark chocolate brown in the dark form with a
lighter torso and darker legs (Groves 2001; Mootnick 2006). This subspecies is
creamy in the light form (Groves 2001). H. l. vestitus are always light with no
dark form and are typically light brown, with a buff back, pale lower back and a
brown head, ventrum and limbs (Marshall & Sugardjito 1986; Groves 2001).
However, due to variation across their distribution, if a specific lar gibbon's
place or origin is unknown, it is difficult to assign it subspecifically based
on morphology (Geissmann 1995). Morphological differences between subspecies
need to be further documented (Brandon-Jones et al. 2004).

Lar gibbons are adapted for arboreal locomotion and usually move through
their environment using brachiation, but also through other forms of movement
(Roonwal & Mohnot 1977; Vereecke et al. 2006). These include walking
(bipedal, tripedal, and quadrupedal), hopping, running (bipedal, tripedal, and
quadrupedal), climbing, swinging, bridging and leaping (Baldwin & Teleki
1976; Carpenter 1976). Lar gibbons are also capable of rapid terrestrial
movement using 7 types of gait even though they are adapted for arboreal
locomotion (Vereecke et al. 2006).

In captivity, lar gibbons have lived up to around 50 years of age (Weigl
2005).

RANGE

Lar gibbons are mainly found in Southeast Asia and in a small portion
of South Asia. They have the greatest north-south range of any of the
gibbons (Bartlett 2007). The species is found in Indonesia, Laos,
Malaysia, Myanmar and Thailand (Brandon-Jones et al. 2004). Lar gibbons
are probably extinct in China but if they still exist, they would only
be found in Southwest Yunnan, their former range (Brandon-Jones et al.
2004; Brockelman & Geissmann 2008; Geissmann 2008). Moving south from
southwest Yunnan, lar gibbons are found in the majority of Thailand excepting
the north-eastern areas of the country. The range extends south through
southern and eastern Myanmar but only east of the Salween River (Brockelman &
Geissmann 2008). They are found through the Malay Peninsula except for a
discontinuity in their distribution between the Perak and Muda Rivers, very
roughly near the Thai-Malay border (Brockelman & Geissmann 2008). Lar
gibbons also exist west of the Mekong River in northwestern Laos and in northern
Sumatra (Brandon-Jones et al. 2004; Brockelman & Geissmann 2008).
Subspecifically, H. l. lar are found in peninsular Malaysia and possibly
Thailand. H. l. carpenteri is found in Myanmar, west Laos, and north
Thailand. H. l. entelloides is found in southeast Myanmar, and in central and
south Thailand (Brandon-Jones et al. 2004). In Indonesia, H. l. vestitus is
found over the northern third of the island of Sumatra (MacKinnon 1984;
Brandon-Jones et al. 2004; Brockelman & Geissmann 2008).

In Thailand, there are probably between 15,000-20,000 lar gibbons (Geissmann
2007).

Perhaps the most important study site of lar gibbons is at Khao Yai,
Thailand, northeast of Bangkok, home to many studies (some long-term)
since the 1970's (Brockelman et al. 1998; Bartlett 2009). The
vegetation type at this site is mostly seasonally wet evergreen rainforest
(Brockelman et al. 1998; Bartlett 2009). Three seasons are experienced in this
part of Thailand; a cool season (November to February), a hot season (March-May)
and a wet season (June-October) (Bartlett 2009). Annual rainfall at this site
averages between 200 and 300 cm (78.7 and 118.1 in) (mostly falling
June-September) and daytime high temperatures usually average between 25°C
and 30°C (77°F and 86°F) year-round. The coldest lows are
usually no colder than 10°C (50°F) (Tangtham 1991 cited in Bartlett
2009; Bartlett 2009).

Lar gibbons are usually found high in the canopy and are rarely found in
the understory (Ungar 1996). At Khao Yai, the average height of feeding trees
was 23.7 meters (77.8 ft) (Bartlett 2009).

ECOLOGY

Lar gibbons eat a large variety of foods, especially fruit, including figs
and other small, sweet fruits, liana fruit, tree fruit and berries but also
young leaves, buds & flowers, new shoots, vines, vine shoots, insects
including mantids and wasps, and even birds' eggs (Carpenter 1940; Ellefson
1974; Raemaekers 1979; MacKinnon & MacKinnon 1980; Ungar 1995; Palombit
1997; Yimkao & Srikosamatara 2006; Bartlett 1999; 2009). They are known to
eat parts of over 100 species of plants (Bartlett 1999; 2009). In general, when
data is combined among study sites, the lar gibbon diet includes fruit (66%),
leaves (24%), flowers (1%), and insects (9%) although in individual studies
there can be some significant variation by locality (see review in Bartlett
2007; Bartlett 2007). Figs often make up a large proportion of the diet, on
average around 27%, but sometimes up to half of the total foods eaten (Palombit
1997; Bartlett 2007). Feeding on figs increases during times that other
preferred resources are scarce (Bartlett 1999). Food transfer between lar
gibbons has been seen often accompanied by begging of one animal for food from
another (Nettelbeck 1998). Most leaves that are eaten are young. One
method that lar gibbons drink water is from tree holes by cupping their
hands (Bartlett 1999).

H. l. carpenteriPhoto: Alan Mootnick

Diet can vary quite a bit with the seasons. For example, at Khao Yai,
non-fig fruits dominated in the diet through the year excepting November and
December. At this study site, flowers are most available during the cool
season, while ripe fruit is most abundant during the hot and wet seasons. At
this study site, ripe fruit is preferred when available, with the variability of
the diet increasing when ripe fruit is less available during the cool season.
However, fruit including figs never fell below 50% of the diet year-round
(Bartlett 2009).

Food competition may exist between lar gibbons and pigtail macaques
(Macaca nemestrina) as the two species have been seen foraging near one another
and sometimes interacting (Whitington 1992). Feeding competition between lar
gibbons and long-tailed macaques (M. fascicularis) and dusky leaf monkeys
(Trachypithecus obscurus) has also been seen (Ellefson 1974). Lar gibbons
compete with sympatric siamangs (Symphalangus syndactylus), the presence of
which usually causes conflict and probably reduces the foraging success of lar
gibbons (Palombit 1996).

Diurnal lar gibbons in Thailand are active for an average of 8.7 hours per
day, leaving their sleeping sites right around sunrise and entering sleeping
tress an average of 3.4 hours before sunset (Bartlett 2009). On average, lar
gibbons spend their days feeding (32.6%), resting (26.2%), traveling (24.2%), in
social activities (11.3%), vocalizing (4.0%) and in inter-group encounters
(1.9%), although actual proportions of activities can change significantly over
the course of the year (Bartlett 2009). Daily, if the morning is clear before
dawn, an adult male will solo call, usually from its sleeping tree. At
sunrise, all group gibbons will awaken, then defecate and urinate while
hanging from a branch. Usually, the group will then move to a feeding
tree. There is normally
a duet call among the adult pair before noon and the rest of the day is spent
alternating between feeding and traveling to new trees to feed. With seasonal
reductions in the amount of available fruit, feeding time increases and,
correspondingly, less time is spent in social activities (Bartlett 2009). A
group pause for about an hour of rest and social activities usually
occurs each day (Bartlett 2009). During the cool season, lar gibbons can often
be found for up to several hours a day in big fig trees (Bartlett 2009).

Average home range is 0.4 km² (0.15 mi²), with a daily path length of 1.4
kilometers (0.87 mi) although there is considerable variation among study sites
(Bartlett 2007). Daily path length tends to increase with increased fruit
availability (Bartlett 1999). Group progressions at some locations are usually
led by the adult male, while at other sites females may do so, and coordinate group
movements as well (Yimkao & Srikosamatara 2006; Barelli et al. 2008a).
Within the home range is a territory defended from other groups averaging around
76% of the home range (Bartlett 2007). The home ranges of different groups
often overlap, sometimes extensively (Ellefson 1974; Reichard & Sommer 1997;
Bartlett 1999).

Sleeping trees are not manipulated and group members usually sleep one to a
tree nearby each other. Often the tallest trees available are chosen for
sleeping and lar gibbons try to avoid notice when moving to sleeping sites,
possibly as a way of reducing predation (Reichard 1998). Often, sleeping trees
are located on steep slopes or on cliffs (Yimkao & Srikosamatara 2006).

While the specific composition of the primate community varies across the
distribution of the lar gibbon, the species can be found living in sympatry with
several other primates and apes, including orangutans (Pongo pygmaeus), siamangs
(S. syndactylus), pileated gibbons (Hylobates pileatus), purple-faced
langurs (Trachypithecus sp.),
Thomas's langur (Presbytis thomasi), slow loris
(Nycticebus coucang),
and several macaque species (Macaca sp.) (Ellefson 1974;
Geissmann 1991; Palombit 1992; Ungar 1995; Palombit 1996; Bartlett 1999; Yimkao
& Srikosamatara 2006).

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